TITLE: GCN GRB OBSERVATION REPORT NUMBER: 446 SUBJECT: GRB991106, near-infrared observations DATE: 99/11/12 18:07:58 GMT FROM: Sylvio Klose at TLS Tautenburg B. Stecklum, S. Klose (Thueringer Landessternwarte Tautenburg), O. Fischer (Universitaets-Sternwarte Jena), R. Lenzen (Max-Planck-Institut fuer Astronomie, Heidelberg), F. J. Vrba, A. A. Henden, C. B. Luginbuhl, B. Canzian, S. E. Levine, H. H. Guetter, J. A. Munn (U.S. Naval Observatory, Flagstaff), A. Castro-Tirado (LAEFF-INTA, Madrid, and IAA-CSIC, Granada), J. Greiner (AIP Potsdam), J. Gorosabel (LAEFF-INTA, Madrid, and University of Amsterdam), and A. Riffeser (Universitaets-Sternwarte Muenchen) report: The error box of GRB 991106 was imaged with the Calar Alto 3.5-m telescope on November 7.799 - 7.841 UT using the near-infrared camera Omega Cass (see http://www.mpia-hd.mpg.de/). The frames were taken in the course of a project whose goal is to measure the degree of linear polarization of GRB afterglows (Klose et al., proceedings 5th Huntsville symposium, to be submitted). The limiting magnitude of the K'-band image is about K'=19 after adding all images taken at different position angles of the wire-grid polarizer. Since the error box is at low Galactic latitude, we report here on the results of a search for very red objects. Polarimetric data will be published at later times. A comparison of the combined K'-band image with I-band images obtained on November 7.9 UT at the Calar Alto 1.23-m telescope and on November 8.2 at the USNO 1.0-m telescope shows an object at coordinates RA (J2000) = 22:24:32.4, DEC = 54:23:51 (+/- 1 arcsec) which has a large I-K' color. The object is inside the original 3.2 arcmin BeppoSAX error circle (Piro et al., GCN #435), but about 10 arcsec outside the BeppoSAX NFI 1.5 arcmin error circle (Antonelli et al., GCN #445). There is one object inside the NFI error circle which is seen both in K' and I, and which is very red. This object is at RA (J2000) = 22:24:39.7, DEC = 54:21:46 (+/- 1 arcsec). Both objects have very faint counterparts on the DSS2 Digitized Sky Survey. They seem to be constant between the two I-band epochs. This cannot be stated with certainty, however. There is no object visible in K' at the position of the radio source reported by Frail et al. (GCN #444). Any such source must be fainter than about K'=19. The preliminary K'-band image is posted on the Tautenburg Web page at http://www.tls-tautenburg.de/research/grb991106.html. This message is citeable.